For the purpose of improving the coke quality and the productivity, in manufacturing a coke for blast furnace using a conventional, i.e., a horizontal type coke oven battery, a method is known, which comprises charging briquettes produced by forming blended raw material coal fines by a compression forming machine (hereinafter referred to as "formed coal"), and carbonizing said formed coal to produce a coke.
According to this method, a coke for blast furnace is produced either by charging a formed coal and coal fines after mixing into a horizontal type coke oven battery, charging a formed coal and coal fines alternately in horizontal layers into a horizontal type coke oven battery, or charging a formed coal only into a horizontal type coke oven battery; and then carbonizing the raw materials thus charged.
In the aforementioned method, in charging a formed coal and coal fines in combination into a horizontal type coke oven battery, pieces of formed coal should be completely agglomerated with surrounding coal fines during the process of carbonization. For this purpose, it is necessary to use raw material coals having a somewhat high fluidity in carbonizing, and this not only imposes certain limits on the range of selection and blending of raw material coals used, but also necessitates troublesome charging practices into the horizontal type coke oven battery.
When only a formed coal is charged into a horizontal type coke oven battery, there is available a wide range of selection and blending of raw material coals used, and the charging into a horizontal type coke oven battery is also easy. In this case, however, the operation of the horizontal type coke oven battery is problematic. More specifically, with a view to facilitating discharge of an already carbonized formed coal (hereinafter referred to as "formed coke"), it is necessary that pieces of formed coke should be mutually agglomerated. On the other hand, however, a formed coke mutually agglomerated too firmly remains in the agglomerated state even after discharging, not separated into pieces. It is therefore desirable that a formed coke produced by charging only a formed coal into a horizontal type coke oven battery, being in a mutually agglomerated state at the time of discharging, should be only slightly agglomerated so as to permit easy separation into pieces after discharging. In a horizontal type coke oven battery, however, the heating rate differs between the zone near the oven walls and the central zone. If the blending ratio of raw material coals is decided on the basis of the central zone, pieces of formed coke in the zone near the oven walls are mutually agglomerated too firmly, and remain in the agglomerated state even after discharging, not permitting separation into pieces. A blending ratio of raw material coals not causing mutual agglomeration of a formed coke, if adopted to avoid the aforementioned drawback, leads to a lower strength of the formed coke. If, on the contrary, the blending ratio of raw material coals is decided on the basis of the zone near the oven walls, pieces of formed coke in the central zone are not mutually agglomerated, thus making it difficult to discharge the produced coke.
For the purpose of obtaining a formed coke in mutual agglomeration as mentioned above, a method has been proposed, which comprises charging only a formed coal produced by blending raw material coal fines so as to give a coking index of 80 to 88 into a horizontal type coke oven battery and carbonizing said formed coal. According to this method, it is not always possible to obtain a satisfactory formed coke in a slight mutual agglomeration. Said coking index is defined as an index calculated by (A + B/10 .times. 100, where:
A: the amount of oversize coke (g) obtained by sieving through a 35 mesh screen a coke produced through carbonization of a mixture consisting of a coal fine with a size of not more than 65 mesh in an amount of 1 g and a coke breeze with a size of 48 to 65 mesh in an amount of 9 g in a crucible at 950.degree. .+-. 20.degree. C for 7 minutes; and PA1 B: the amount of oversize coke (g) obtained by sieving further through a 48 mesh screen the undersize coke obtained through said 35 mesh screen.